The present invention relates to a piston engine powertrain, and more particularly to a powertrain which transmits power from a piston of an internal combustion engine to an output shaft. This invention is an improvement over the powertrain disclosed in U.S. Pat. No. 5,626,113, the disclosure of which is incorporated herein by reference.
Conventional powertrains in use with piston engines employ a connecting rod which is pivotally connected between each piston and a crankshaft which is an output shaft. Such constructions have many shortcomings. A very large reciprocating mass is involved, and large friction losses are created. Piston rings and lubrication oil are required within the cylinder. Because lubrication oil may deteriorate, the cylinder wall temperatures cannot be high enough to prevent flame quenching on the cylinder wall. The piston rings create areas where some portion of the fuel in the cylinder may not be burned effectively. The inherent inability of such engines to control the high firing temperature leads to NOx formation, which is very undesirable.
With conventional arrangements utilizing a connecting rod and crankshaft to transmit power, the cylinder volume of a four stroke combustion-ignition (CI) engine varies in a fixed pattern in accordance with the output shaft rotating angle. Therefore, an engine designer does not have the ability to choose an appropriate piston speed for each engine cycle event for the same average piston speed. It is therefore desirable to provide a construction whereby an engine designer has the freedom to choose the piston movement throughout an engine cycle. This is a principal objective of the present invention.
In today's mid-size sedans only one-third of the engine power is required to maintain a highway speed of 70 mph. Full power is only required for quick acceleration and hill climbing. Hybrid engines have been developed wherein extra power provided by an IC engine produces electrical power which may be stored by a battery so that electric power may be used to drive the output shaft only when peak power is provided. Such hybrid engines require additional components and the complexity and cost thereof is substantially increased. However, a conventional six-cylinder engine may accomplish the desired result by deactivating four cylinders when only one-third of the total power of the engine is required.
The high cycle efficiency of an overexpanded cycle has long been recognized. However, such a cycle requires a longer piston stroke for expansion and exhaust processes and a shorter piston stroke for intake and compression processes. This has not been successfully accomplished in the prior art. It is, therefore, an important objective to provide a construction whereby an overexpanded cycle can be obtained.